Directional radio transmitter



' May 13, 194-1. E, MULLER 2,241,918

DIRECTIONAL RADIO TRANSMITTER Filed March 14, 1939 H/GH FREQUENCY 9 GENE/5470)? Patented May 13, 1941 UNETED STATES orrics DIRECTIONAL RADIO TRANSMITTER Application March 14, 1939, Serial No. 261,709 In Germany March 23-, 1938 1 Claim.

As is well known, course lines for navigation purposes may be obtained by means of directional radiation characteristics or patterns which are produced alternately in the rhythm of complementary signals, such as the Morse signals a-n or dot-dash signals, and which overlap one another. A non-directional receiver acts to compare the field intensities of the two radiation patterns. The transmitting arrangements for effecting this method usually comprise two directional antennae positioned angularly with respect to each other and which are alternately rendered effective and ineffective. Also an arrangement is known in which a directive system having a double-circular radiation characteristic and a non-directive antenna having a circular characteristic are alternately combined with each other in phase coincidence and phase opposition. This arrangement acts to produce cardioidshaped radiation patterns which on phase reversal of the directive system are displaced by 180 degrees.

The invention is concerned with the so-called keying of directional radio transmitters used for producing course lines of equal field intensity. In such arrangements difliculties arise through the requirement that each directional antenna system should be rendered effective as soon as the other is rendered ineffective. The relays or collectors hitherto employed for this purpose are possessed of a bad contact operation since with the keying effected in the antenna circuit the entire high frequency power is to be overcome by them.

In accordance with the invention the said disadvantages are avoided in such a manner that the keying is efiected by alternately tuning and detuning the antenna circuit with the aid of condensers having a rotary member. I

One embodiment of the invention is shown in the accompanying drawing in which Fig. 1 represents the circuit arrangement of the novel keying device, while Fig. 2 is a view of a keying condenser that forms part of the arrangement shown in Fig. 1.

In the case represented by way of example the mutually overlapping radiation patterns pro duced alternately by the keying operation, are set up by combining a double-circular radiation pattern with the circular radiation pattern of a linear antenna. In the four angles of a square four single antennae I, 2, 3, 4 are arranged. These are in pairs diagonally interconnected over goniometer field coils 5, 6 to form a directive system. The third goniometer coil 1, coupled to the coils 5, 6, is fed from a high frequency generator 9 over a keying device that forms part of the invention. In the middle between the antennae I, 2, 3, 4 a linear antenna I0 is disposed which is continually fed from generator 9 over a coil II. The double-cricular radiation characteristic peculiar to the said directive system and the circular characteristic of antenna I0 cooperate in a manner to produce cardioidshaped radiation patterns which on reversal of the current direction in coil 1 are displaced by degrees.

The keying device 8 is in the nature of a bridge connection in whose middle arm the coil 1 is included. Device 8 comprises a keying condenser !2 which has two stators l3, I4 and a rotor l5. Rotor I5 is rotated by a motor IS. The two lateral bridge arms are by oscillatory circuits I1, l8 so tuned that the bridge arm at I 8 is in resonance with the transmitter frequency whenever rotor I5 is facing the stator l3, while with rotor l5 facing the stator Hi the bridge arm at I! will be resonant therewith. In this way, either one or the other bridge arm will be nonresonant, namely that arm which at the time is out of engagement with rotor I5. The tuning may of course be such. that each bridge arm is resonant whenever the rotor is turned out of engagement with the stator to which the respective bridge arm is connected, becoming detuned when the rotor is turned to engage the stator. The stators I3, M are so formed as to cause complementary signals to be produced. In the case represented the stator 13 acts to produce a dot signal whereas stator I4 causes a dash signal to be originated. When rotor l5 changes from one stator to the other the current direction in coil 1 is reversed. In consequence of this, the phase of the double-circular radiation pattern will be reversed in its turn, the directive pattern now radiated being displaced by 180 degrees with respect to the former.

An example of the keying condenser I2 is shown in Fig. 2 in which the constituent parts thereof are denoted by the reference characters used in Fig. 1. The number of revolutions of the rotor corresponds to the signal frequency or forms an integral ratio therewith.

The keying arrangement may of course be such that a separate keying condenser is provided for each kind of signals. The revolutions of the condensers so provided are calculated to depend upon each other.

In order to produce rotating course lines instead of stationary ones, it is only necessary to rotate coil 1. the drive of the condenser, that is, by motor [5, for instance. In such case a constant ratio of the number of revolutions of the coil 1 and rotor I5 is insured by suitable transmission gearing.

What is claimed is:

A radio transmitter comprising first and sec-- ond circuits each including a capacity, rotary capacity varying means for alternately increasing one and then the other of said capacities, a high frequency source coupled to both said circuits for supplying high frequency energy thereto, an omni-direotional radiator continuously fed from said source, tuning means for adjusting each of said circuits to such reactance that said circuits become alternately resonant t0 the frequency of said source in response to the alternate This coil is preferably driven by increase of one and then the other of said capacities, a vario-coupler of the goniometer type having two stationary inductors and one rotatable inductor, said rotatable inductor being coupled to both said tuned circuits in such sense as to receive energy therefrom alternately in one phase and then the opposite phase in response to said alternate increase of one and then the other of said capacities, four vertical antennae arranged in two pairs and coupled to said two stationary inductors of said vario-coupler, and means for continuously rotating said rotatable inductor of said vario-coupler and said rotary capacity varying means with a constant ratio of rotary speeds.

ERNST MiiLLER. 

